Electroplating is used in the manufacture of, e.g., thin film inductive heads used in magnetic recording systems, such as disk drives, as well as micromechanical structure fabrication, such as for microactuators and magnetic micromotors. Electroplating generally involves electroplating on a substrate, through a patterned photosensitive resist film, with the desired feature and surrounding plating field. The surrounding plating field is not part of the desired feature, but is used to ensure good thickness and alloy composition uniformity in small features.
When electroplating a layer with a large tensile stress, such as with a thick layer of high magnetic moment material, the surrounding plating field has a tendency to delaminate. Delamination is generally undesirable even when it occurs in an area other than the desired feature, i.e., in the plating field. An underlying adhesion layer is sometimes used to help prevent delamination. Nevertheless, delamination may still occur when a layer has a large tensile stress.
FIGS. 1 and 2 illustrate a top plan view and cross sectional view (along line A-A) of a conventionally electroplated substrate 100 and a delaminated plating field 110. As illustrated, the substrate 100, which may be, e.g., alumina, is covered with an adhesion layer 102 and a seed layer 104. As illustrated in FIG. 2, a thick layer 106 of high moment material, such as CoFe, is electroplated over the adhesion and seed layers 102, 104.
A portion of the plated layer 106 forms the desired feature 108 (shown in FIG. 1) under manufacture, while another portion of the plated layer 106 forms the plating field 110 (shown in FIG. 1). The plating field 110 surrounds the feature 108 and is separated by a non-plated area 109. The layer 106 is conventionally formed using a resist pattern to define the desired feature 108 and the field portion 110.
Plated high moment materials, e.g., CoFe alloys of greater than or equal to 2.4 T moment, have a large amount of tensile stress. When a relatively thick layer of the high moment material is plated, the stress is sufficient to delaminate the layer from underlying layers or substrate, particularly near any sharp corner, angular or non-smooth surfaces. Thus, as illustrated in FIGS. 1 and 2, the corners 110a and 110b of the plating field 110 have become delaminated.
As is well understood in the art, unintentional delamination of a plated layer is undesirable. For example, an undesirable under-filling of the area under the delaminated portion of the layer may occur during subsequent processing. Additionally, the stress on the plated layer may be sufficient to damage the underlying substrate 100, as illustrated at corner 110a in FIG. 2.
For a given stress, the delamination force in an electroplated layer is a function of the thickness of the layer. By way of example, a layer with a stress of approximately 400 MPa will typically delaminate at a thickness of approximately 2 μm and a layer with a stress of approximately 600 MPa will typically delaminate at a thickness of approximately 0.5 to 1 μm. Accordingly, the delamination of an electroplated layer of material having a given stress is prevented conventionally by limiting the thickness of the plated layer. By way of example, to avoid the delamination of a high moment layer, e.g., with a moment of 2.4 T (which has a stress of 400 Mpa); the maximum thickness of the plating field is limited to approximately 2 μm. Unfortunately, it is sometimes desirable to plate a layer of high stress material to a thickness that is greater than its conventional maximum thickness.
Accordingly, what is needed is an improvement to electroplating that decreases the chance of delamination of the plated layer.